The objective of the proposed research is to study the mechanism of interference by defective influenza virus (DI virus) particles. We have developed a system for quantitative studies of viral interference. We have further found that DI particles interfere with VRNA synthesis and not with CRNA synthesis. We want to find out what is the molecular mechanism of the interference and which of the following subviral components - DI-RNP, DI-viral RNA or DI-CRNA - is the interfering molecule and finally, we would like to determine how much information is lost in DI viral RNA compared to infectious viral RNA.